It is well known that charged particules may be accelerated by an electric field established between two electrodes. Where high energy levels of, for example, 5,000 eV are required, high potential differences of 5,000 or more volts are required to establish the necessary electric field. However, many factors place limitations on the maximum potential differences which can, as a practical matter, be provided. For example, ionization or breakdown of the gas is one limiting factor, and surface or material breakdown of the insulation which spaces the electrodes is another limiting factor.
The voltage at which ionization occurs is a function of the product of the gas pressure and the distance between the electrodes across which the voltage is applied, which product is hereinafter referred to as Pd. A plot of breakdown voltage vs. Pd provides the well-known Paschen Curve wherein breakdown voltage decreases with an increase in Pd in the region to the left of the minimum point of the curve. For maximum acceleration it is necessary to maintain the breakdown voltage as high as possible, but the minimum value of the pressure within the device is limited by constraints elsewhere in the device, such as when it is desired to use a hollow cathode of specific dimensions as an electron source. Similarly, since the surface material breakdown voltage decreases in proportion to the distance d between the electrodes, the minimum value of d is limited by the insulation materials available. Therefore, in the prior art the maximum accelerating voltage has been limited by the minimum pressure and minimum spacing available in the device.
In order to obtain high-energy electrons for exciting the luminescent materials on the display screen of a cathodoluminescent flat-panel display and for other purposes, it would be desirable to increase the breakdown voltage between electrodes for a given value of Pd. As a consequence, high accelerating voltages and resulting higher electron velocities can be provided with a concomitant increase in the brightness and luminous efficiency of the display.